Primary coatings for optical glass fibers including poly(carbonate-urethane) acrylates

ABSTRACT

Photocurable liquid coating compositions adapted to provide primary coatings for optical glass fibers are disclosed. These compositions comprise polycarbonate-based acrylate-terminated polyurethane, an acrylate of an unsubstituted or C 1  -C 10  alkyl substituted phenol that is alkoxylated with a C 2  -C 4  alkylene oxide and at least one alkylacrylate having a T g  below about -45° C. Films produced from these ultraviolet light curable compositions are flexible and possess good water resistance and good wet adhesion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 07/730,589,filed Jul. 15, 1991 and now abandoned, which is a continuation-in-partof U.S. Ser. No. 07/403,596, filed Sep. 6, 1989 and now abandoned.

TECHNICAL FIELD

This invention relates to primary coatings for optical glass fibers thatare characterized by greater cure speed, enhanced cured film adhesionand stability, reduced water absorption and superior low temperatureperformance.

BACKGROUND OF THE INVENTION

Optical glass fibers are frequently coated with two superposedphotocured coatings. The coating which contacts the glass is arelatively soft, primary coating. The outer, exposed coating is a muchharder secondary coating that provides desired resistance to handlingforces, such as those encountered when the fiber is cabled.

The coating of optical glass fibers with photocured coatingcompositions, usually using ultraviolet light, is well known today.Photocuring compositions are selected because of their rapid cure speed.Faster cure speed is generally desirable to increase the production ofoptical glass fibers.

Coatings produced from conventional compositions including(meth)acrylate-terminated polyurethanes are much too hard to be utilizedas primary coatings and exhibit poor adhesion and resistance tomicrobending especially at low service temperatures. When a polyetheracrylate monomer having a low glass transition temperature (T_(g)) isadded to these compositions in an amount sufficient to provide adequateflexibility, the water resistance and adhesion of the coating areusually reduced which is undesirable.

It is also desirable to further increase the cure speed of thephotocuring composition while retaining the capacity of the curedprimary coating to adhere to the glass fiber surface and to resist waterabsorption.

SUMMARY OF THE INVENTION

The present invention provides compositions suitable as a primaryoptical glass fiber coating that comprise an acrylate-terminatedpolyurethane, an acrylate of an alkoxylated phenol and an acrylatehaving a low T_(g). The coatings produced from these compositionsexhibit good adhesion, flexibility, water resistance and low temperaturemicrobending resistance.

A photocurable liquid coating composition adapted to provide a primarycoating for an optical glass fiber is disclosed. The coating compositioncomprises (1) about 30 to about 80 weight percent, based on the totalweight of the coating composition, of an acrylate-terminatedpolyurethane (the "acrylated polyurethane") having a number averagemolecular weight of about 2,500 to about 8,000 daltons, said acrylatedurethane being the reaction product of a prepolymer having a numberaverage molecular weight of about 700 to about 2,000 daltons where theprepolymer is selected from the group consisting of polycarbonates andmixtures of polycarbonates and polyethers having an average of at leasttwo groups that are reactive with an isocyanate group, a diisocyanateand a hydroxy acrylate; (2) about 20 to about 60 weight percent of anacrylate of an unsubstituted or C₇ -C₁ alkyl substituted phenol that isalkoxylated with a C₂ -C₄ alkylene oxide and contains about 1 to about 5moles of the oxide per mole of phenol; and ( 3) about 5 to about 30weight percent of at least one alkylacrylate having a glass transitiontemperature (T_(g)) below about -45° C.

The composition can further include a monoethylenically unsaturatedmaterial having a T_(g) greater than about 40° C. and a strong capacityfor hydrogen bonding that is present in an amount in the range of about1 to about 15 weight percent, based on the total weight of the coatingcomposition.

Conventional photoinitiators are also present to initiate polymerizationby ultraviolet light and visible light near the ultraviolet wavelengthrange.

Coatings produced on optical glass fibers from the present coatingcomposition provide good adhesion and enhanced hydrolytic and thermalstability, reduced water absorption and superior low temperatureperformance, e.g., improved resistance to microbending, as compared toconventional primary coatings.

As previously discussed, poly ether acrylate monomers can be utilized tointroduce flexibility in coatings produced from compositions thatinclude acrylate-terminated polyurethanes. However, these polyetheracrylate monomers usually reduce the water resistance and adhesion ofthe coating. In contradistinction, the present composition utilizesphenol-based acrylate polyethers, identified as component "(2)" of thecomposition, to introduce softness and flexibility into coatingsproduced from an acrylated polyurethane while maintaining a desirabledegree of water resistance and adhesion. This use of polyethers isunconventional because polyethers typically reduce water resistance andadhesion. The cure speed is also increased and this is desirable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although this invention is susceptible to embodiments in many differentforms, preferred embodiments of the invention are shown. It should beunderstood, however, that the present disclosure is to be considered asan exemplification of the principles of the invention and is notintended to limit the invention to embodiments illustrated.

A photocurable liquid coating composition adapted to provide a primarycoating for an optical glass fiber is disclosed. The coating compositioncomprises: (1) about 30 to about 80 weight percent, based on the totalweight of the coating composition, of an acrylate-terminatedpolyurethane (acrylated polyurethane) having a number average molecularweight of about 2,500 to about 8,000 daltons and being the reactionproduct of a prepolymer having a number average molecular weight ofabout 700 to about 2,000 daltons where the prepolymer is selected fromthe group consisting of polycarbonates and mixtures of polycarbonatesand polyethers having an average of at least two groups that arereactive with an isocyanate group, a diisocyanate and a hydroxyacrylate; (2) about 20 to about 60 weight percent of an acrylate of anunsubstituted or C₇ -C₁₀ alkyl substituted phenol that is alkoxylatedwith a C₂ -C₄ alkylene oxide and contains about 1 to about 5 moles ofthe oxide per mole of phenol (acrylate of the alkoxylated phenol); and(3) about 5 to about 30 weight percent of at least one alkylacrylatehaving a glass transition temperature (T_(g)) below about -45° C.

The term "dalton", in its various grammatical forms, defines a unit ofmass that is 1/12th the mass of carbon-12.

The term "acrylate", and various grammatical forms thereof, identifiesesters that are the reaction product of acrylic acid with a hydroxygroup-containing compound.

The term "alkylacrylate" identifies alkyl substituted acrylates, as forexample, hexyl acrylate 2-ethylhexyl acrylate, heptyl acrylate, n-octylacrylate and isooctyl acrylate.

The term "glass transition temperature, in its various grammaticalforms, is defined as the temperature at which the homopolymer of thereferred to material changes from a vitreous state to a plastic state.

The acrylate-terminated polyurethane is the reaction product of aprepolymer, an organic diisocyanate and a hydroxy acrylate.

The prepolymer is a carbon chain that can comprise oxygen and/ornitrogen atoms to which the terminal acrylate functionality is added byuse of the diisocyanate. Selection of the prepolymer can affect thephysical properties of the coatings produced from theoligomer-containing composition.

The prepolymer has on average at least about two prepolymer functionalgroups that are reactive with the isocyanate group, e.g., a hydroxy,mercapto, amine or similar group. Presently, a preferred prepolymerfunctional group is the hydroxy group.

The number average molecular weight of the prepolymer is about 700 toabout 2,000, preferably about 800 to about 2,000, daltons.

Prepolymers are selected from the group consisting essentially ofpolycarbonates, and mixtures of polycarbonates and polyethers.

Albeit all of the above-described prepolymers provide improved resultswhen utilized with the acrylate of the alkoxylated phenol, thepolycarbonate diols give superior results, especially from thestandpoint of hydrolytic and oxidative stability, and thus arepreferred.

The polycarbonate diols are conventionally produced by the alcoholysisof diethylcarbonate or diphenylcarbonate with a diol. The diol is analkylene diol having about 2 to about 12 carbon atoms, e.g., 1,4-butanediol, 1,6-hexane diol, 1,12-dodecane diol and the like, preferably about4 to about 8 carbon atoms. Mixtures of these diols can also be utilized.The polycarbonate diol can contain ether linkages in the backbone inaddition to carbonate groups. Thus, polycarbonate copolymers of alkyleneether diols and the previously described alkylene diols are suitable.Suitable alkylene ether diols include triethylene glycol, tripropyleneglycol and the like. These copolymers produce cured coatings thatexhibit a lower modulus and also inhibit crystallinity of the liquidcoating composition, as compared to polycarbonate diol homopolymers.Admixtures of the polycarbonate diols and polycarbonate copolymer diolscan also be utilized.

Suitable polycarbonate diols include Duracarb 122, commerciallyavailable from PPG Industries and Permanol KM10-1733, commerciallyavailable from Permuthane, Inc., MA. Duracarb 122 is produced by thealcoholysis of diethylcarbonate with hexane diol.

Illustrative polyesters include polybutylene adipate, polycaprolactonesand the like.

Illustrative polyethers include poly(propylene oxide),poly(tetramethylene glycol) and the like.

A wide variety of diisocyanates alone or in admixture with one anothercan be utilized. Representative diisocyanates include isophoronediisocyanate (IPDI), toluene diisocyanate, methylene diphenyldiisocyanate, hexamethylene diisocyanate, cyclohexylene diisocyanate,methylene dicyclohexane diisocyanate, 2,2,4-trimethyl hexamethylenediisocyanate, m-phenylene diisocyanate, 4-chloro-1,3-phenylenediisocyanate, 4,4'-biphenylene diisocyanate, 1,5-naphthylenediisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylenediisocyanate, 1,10-decamethylene diisocyanate, 1,4-cyclohexylenediisocyanate, and the like. A preferred diisocyanate is IPDI.

The hydroxy acrylate can be a monoacrylate or a polyacrylate. Monohydricmonoacrylates are presently preferred. The reaction of the isocyanategroup with a hydroxy group of the hydroxy acrylate produces a urethanelinkage which results in the formation of an acrylate terminatedurethane.

Suitable monohydric acrylates are the hydroxy C₂ -C₄ alkyl acrylates andpolyacrylates. Illustrative of these acrylates are 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, glyceryl diacrylate, and the like.Mixtures of these acrylates are also suitable. The methacrylatecounterparts of the above acrylates can also be utilized.

The reaction of the prepolymer, the diisocyanate and the hydroxyacrylate is conventional and is performed in a suitable vessel. The moleratio of prepolymer diol: diisocyanate: hydroxy acrylate can be in arange of about 1:2:2, respectively, to about 5:6:2, respectively. Thesereactants together with the low T_(g) alkyl acrylate diluent monomer areadmixed in a vessel with a minor amount of a catalyst for the urethaneforming reaction, e.g., about 0.03 to about 0.1, preferably about 0.04,weight percent of dibutyl tin dilaurate. A sparge of dry gas, e.g., dryair, nitrogen, carbon dioxide or the like, is utilized to ensure thereis no moisture present which can adversely affect the reaction. Thereaction is conducted at a temperature of about 40° to about 80° C. fora time period sufficient to consume substantially all of the hydroxyfunctionality of the prepolymer diol and the hydroxy acrylate and thefree nitrogen-carbon-oxygen groups (NCO) of the diisocyanate.

A preferred method of producing the acrylated polyurethane is to admixthe diisocyanate, the hydroxy acrylate, the low T_(g) alkyl acrylatediluent monomer, and the catalyst in the vessel. The sparge is insertedinto the admixture. The reaction is conducted at a temperature at thelower end of the above temperature range, e.g., about 40° to about 60°C., for a time period sufficient to consume substantially all of thehydroxy functionality of the hydroxy acrylate. This time period istypically between about 1 and about 3 hours. After substantially all ofthe hydroxy functionality is consumed, the prepolymer is introduced intothe vessel with continued admixing and the temperature is increased tothe upper end of the above temperature range, e.g., about 60° to about80° C. This temperature is maintained for a time period sufficient toconsume substantially all of the free NCO and the prepolymer functionalgroups. This time period typically is between about 7 and about 10hours.

The number average molecular weight of the acrylated polyurethane isabout 2,500 to about 8,000, preferably about 3,000 to about 7,000daltons.

The coating composition also includes the acrylate of the unsubstitutedor C₇ -C₁₀, preferably C₈ -C₉, alkyl substituted phenol that isalkoxylated with a C₂ -C₄ alkylene oxide so that it contains about 1 toabout 5 moles of the oxide per mole of the phenol. Preferably, theacrylate of the alkoxylated phenol contains about 3.5 to about 4 molesof oxide per mole of the phenol.

Suitable alkylene oxides include ethylene oxide, propylene oxide,butylene oxide, and mixtures thereof. Presently, ethylene oxide ispreferred.

Representative alkoxylated acrylates include phenoxyethyl acrylate,ethoxylated nonylphenol acrylate and propoxylated nonylphenol acrylate.

Commercially available illustrative acrylates o the alkoxylated phenolinclude alkoxylated nonyl phenol acrylates such as Aronix M-111, AronixM-113 and Aronix M-117 from Toa Gosei, Japan.

The coating composition further includes at least one alkylacrylatehaving a T_(g) below about -45° C., preferably below about -60° C. TheT_(g) of the alkylacrylate can be as low as about -90° C. Thisalkylacrylate enhances low temperature microbending resistance.

Suitable alkylacrylates include n-hexylacrylate, 2-ethylhexyl acrylate,heptyl acrylate, n-octyl acrylate, isooctyl acrylate, n-nonyl acrylateand the like. Mixtures of these akylacrylates are also suitable.

The coating composition can further include a monoethylenicallyunsaturated material having a high T_(g) and a strong capacity forhydrogen bonding. These monoethylenically unsaturated materialstypically have a T_(g) greater than about 40° C. and are illustrated byN-vinyl monomers such as N-vinyl pyrrolidone, N-vinyl caprolactam,mixtures thereof and the like. The T_(g) of the monoethylenicallyunsaturated material can be as high as about 120° C.

The wavelength of the light utilized to cure the coating compositions ofthe present invention can vary somewhat depending upon thephotoinitiator selected. In present practice, the light utilized isusually in the ultraviolet range which extends from about 200 to about400 nanometers (nm) however, light of a longer wavelength, e.g., lighthaving a wavelength of up to about 600 nm, preferably up to about 520nm, can be utilized.

The photoinitiators utilized are conventional components of lightcurable ethylenically unsaturated coatings. Preferred photoinitiatorsare aryl ketones, e.g., benzophenone, acetophenone, diethoxyacetophenone, benzoin, benzil, anthraquinone, and the like. A commercialphotoinitiator is illustrated by Irgacure 184 which is hydroxycyclohexylphenyl ketone and is available from Ciba-Geigy Corp., Ardsley, NY.

Volatile organic solvents are preferably not utilized in the presentcoating composition.

The acrylated polyurethane is present in the composition in an amount inthe range of about 30 to about 80, preferably about 30 to about 60weight percent, based on the total weight of the coating composition.

The acrylate of the alkoxylated phenol is present in the coatingcomposition in an amount in the range of about 20 to about 60,preferably about 20 to about 35 weight percent, based on the totalweight of the coating composition.

The akylacrylate having a T_(g) less than about -45° C. is present in anamount of about 5 to about 30, preferably about 10 to about 20 weightpercent, based on the total weight of the coating composition.

The monoethylenic material having a high T_(g) can be present in thecoating composition in a range of about 1 to about 15, preferably about2 to about 4 weight percent, based on the total weight of the coatingcomposition.

The photoinitiator is present in the coating composition in a range ofabout 0.5 to about 6, preferably about 1 to about 4 weight percent,based on the total weight of the coating composition.

The viscosity of the coating composition, as measured at a temperatureof 25° C. using a Brookfield viscometer, is about 3,000 to about 12,000centipoise (cp), preferably about 4,000 to about 10,000 cp.

It is presently believed that the polyether groups present in theacrylate of the alkoxylated phenol function to soften the cured coatingand provide adequate adhesion to the glass without reducing the waterresistance. This is an unexpected result as typically ether groupsintroduce water sensitivity which reduces water resistance and wetadhesion.

The coating composition can further include conventional adhesionpromoters, stabilizers and inhibitors.

Silane coupling agents are conventional adhesion promoters and typicallycan be present in an amount of about 1 weight percent. Illustrativesilane coupling agents include gamma methacryloxypropyl trimethoxysilane, commercially available from Huls, Bristol, PA, under the tradedesignation MEMO and gamma mercaptopropyl trimethoxy silane which iscommercially available from Union Carbide under the designation A-189.Conventional stabilizers such as hindered amines which provideultraviolet stability for the cured composition can be present inamounts less than about 1 weight percent. Illustrative stabilizersinclude bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate which iscommercially available from Ciba-Geigy Corp., Ardsley, NY, under thetrade designation Tinuvin 770 and thiodiethylene(3,5-di-tert-butyl-4-hydroxy) hydrocinnamate, also commerciallyavailable from Ciba-Geigy Corp under the trade designation IRGANOX 1035.Free radical polymerization during production of the acrylatedpolyurethane can be inhibited by the use of an agent such asphenothiazine or butylated hydroxytoluene in an amount less than about0.1 weight percent.

The present compositions can be applied to glass fibers utilizingconventional processes.

The following examples are presented by way of illustration and notlimitation.

EXAMPLE 1 Comparison of Two Coating Compositions

The acrylate-terminated polyurethane was prepared by admixing2-hydroxyethyl acrylate, isophorone diisocyanate, dibutyl tin dilaurate,octyl/decyl acrylate, and phenothiazine in the amounts disclosed atTABLE I, below, in a suitable vessel. Agitation and a dry air spargewere provided and maintained during the reaction. The temperature of theadmixture was elevated to about 40° C. and maintained at thattemperature for about 2 hours. Thereafter, the polycarbonate diol wasintroduced into the vessel and mixed with the admixture. The temperatureof the mixture was elevated to about 70° C. and maintained at thattemperature for a time period sufficient to consume substantially all ofthe free NCO.

                  TABLE I                                                         ______________________________________                                        ACRYLATE-TERMINATED POLYCARBONATE                                             DIOL-BASED POLYURETHANE                                                       Component        Parts (by weight)                                            ______________________________________                                        Polycarbonate diol.sup.1                                                                       55.50                                                        2-hydroxyethyl acrylate                                                                         5.46                                                        Isophorone diisocyanate                                                                        19.01                                                        Octyl/decyl acrylate.sup.2                                                                     19.94                                                        Dibutyltin dilaurate                                                                            .06                                                         Phenothiazine     .03                                                         ______________________________________                                         .sup.1 Permanol KM 101733, commercially avaliable from Permuthane             Coatings, Peabody, MA.                                                        .sup.2 ODA, Commmercially available from Radcure Specialties Inc.,            Louisville, KY.                                                          

Aliquots of the above described acrylated polyurethane were admixed withvarious proportions of the other components utilized in the coatingcomposition to produce the present coating compositions A and B. Theproportion of these other components and of the acrylated polyurethaneare presented in TABLE II.

                  TABLE II                                                        ______________________________________                                        COATING COMPOSITIONS                                                                           (Parts by weight)                                            Component          A        B                                                 ______________________________________                                        Acrylated polyurethane.sup.1                                                                     57.0     62.0                                              Acrylate of an     33.0     --                                                alkoxylated phenol.sup.2                                                      Phenoxyethyl acrylate                                                                            --       32.9                                              N-vinyl pyrrolidone                                                                              4.0      --                                                Irgacure 184.sup.3 4.0      2.0                                               Lucirin TPO.sup.4  --       1.0                                               Silane.sup.5       1.0      1.0                                               Tinuvin 292.sup.6  0.5      0.5                                               Irganox 245.sup.7  0.5      --                                                Irganox 1035.sup.8 --       0.5                                               Polycat DBU.sup.9  --       0.1                                               ______________________________________                                         .sup.1 The acrylated polyurethane of TABLE I was utilized.                    .sup.2 An alkoxylated nonyl phenol acrylate, commercially available from      Toa Gosei, Japan under the trade designation Aronix M113.                     .sup.3 An aryl ketone photoinitiator, commercially available from             CibaGeigy Corp., Ardsley, NY.                                                 .sup.4 An acylphosphine oxide photoinitiator, commercially available from     BASF Corp., Germany.                                                          .sup.5 An adhesion promoter, commercially available from Huls, Bristol, P     under the trade designation Dynasylan MEMO.                                   .sup.6 A stabilizer, commercially available from CibaGeigy Corp., Ardsley     NY.                                                                           .sup.7 A stabilizer, commercially available from CibaGeigy Corp., Ardsley     NY.                                                                           .sup.8 A stabilizer, commercially available from CibaGeigy Corp., Ardsley     NY.                                                                           .sup.9 An amine catalyst, commercially available from Air Products and        Chemicals, Inc., Allentown, PA.                                          

Compositions A and B of TABLE II were prepared by admixing thecomponents and mixing in the ingredients while heating to 60° C. for 20minutes.

The coating compositions A and B are well adapted to provide a primarycoating for optical glass fibers. This was not previously possible usingthe acrylated polyurethanes utilized in compositions A and B becausemodification of conventional acrylated polyurethane containingcompositions to improve flexibility and softness resulted in a loss inwater resistance, cure speed, and/or adhesion to glass.

The cure speed [Joules/square centimeter (J/sq cm)] and physicalproperties, i.e., modulus [megapascals (MPa)] and dry and wet adhesion(grams), are presented in TABLE III, below. The procedures fordetermining the cure speed and physical properties are describedhereinafter.

                  TABLE III                                                       ______________________________________                                        CURE SPEED AND PHYSICAL PROPERTIES                                            Coating   Cure Speed Modulus   Adhesion-dry/wet                               Composition                                                                             (J/sq cm)  (MPa)     (grams)                                        ______________________________________                                        A         0.5        2.0        60/40                                         B         0.4        2.1       170/70                                         ______________________________________                                    

The cure speed [Joules/square centimeter (J/sq cm)] indicates the numberof J/sq cm required to obtain 95% of ultimate modulus of a 3 mil thickcoating utilizing a "D" lamp from Fusion Curing Systems, Rockville, MD.The "D" lamp emits radiation having a wavelength of about 200 to about470 nanometers with the peak radiation being at about 380 nanometers andthe power output thereof is about 300 watts per linear inch.

The cure speeds obtained are considered rapid by industrial standards.The optical glass fiber coating industry currently utilizes primarycoating composition having cure speeds of about 1.0 J/sq cm.

A film for determination of the modulus of the coating was prepared bydrawing down a 3 mil coating on glass plates using a Bird bar fromPacific Scientific, Silver Spring, MD. The coating was cured using the"D" lamp. The coating was cured at a dose of about 1 J/sq cm whichprovided complete cure. The film was then conditioned at 23°±2° C. and50±5% relative humidity for a minimum time period of 16 hours.

Six, 0.5 inch wide test specimens were cut from the film parallel to thedirection of the draw down. Triplicate measurements of the dimensions ofeach specimen were taken and the average utilized. The modulus of thesespecimens are then determined using an Instron Model 4201 from InstronCorp., Canton, MA operated in accordance with the instructions providedtherewith.

To determine the dry and wet adhesion of a film to glass, films wereprepared by drawing down 3 mil coatings on glass plates using the Birdbar. The coatings were cured using the "D" lamp.

The films were then conditioned at a temperature of 23±2° C. and arelative humidity of 50±5% for a time period of 7 days. A portion of thefilm was utilized to test dry adhesion. Subsequent to dry adhesiontesting, the remainder of the film to be tested for wet adhesion wasfurther conditioned at a temperature of 23±2° C. and a relative humidityof 95% for a time period of 24 hours. A layer of a polyethylenewax/water slurry was applied to the surface of the further conditionedfilm to retain moisture.

The adhesion test was performed utilizing an apparatus including auniversal testing instrument, e.g., an Instron Model 4201 commerciallyavailable from Instron Corp, Canton, MA, and a device, including ahorizontal support and a pulley, positioned in the testing instrument.

After conditioning, sample specimens that appeared to be uniform andfree of defects were cut in the direction of the draw down. Eachspecimen was 6 inches long and 1 inch wide and free of tears or nicks.The first one inch of each specimen was peeled back from the glassplate. The glass plate was secured to the horizontal support with theaffixed end of the specimen adjacent to the pulley. A wire was attachedto the peeled-back end of the specimen, run along the specimen and thenrun through the pulley in a direction perpendicular to the specimen. Thefree end of the wire was clamped in the upper jaw of the testinginstrument which was then activated. The test was continued until theaverage force value becomes relatively constant.

EXAMPLE II Preparation and Evaluation of Additional Oligomers

Oligomer 1 1596.23g Isophorone diisocyanate, 1438.64 g Isodecylacrylate,2.25 g phenothiazine, and 4.49 g Dibutyltin dilaurate were charged to a22 liter round bottom glass flask fitted with a stirrer, dry air sparge,thermometer, reflux condenser, a heating mantle, and an addition funnel.477.24 g 2-hydroxyethyl acrylate were added dropwise from the additionfunnel over a 1 hour period with the flask temperature rising from 30°C. to 43° C. After a 1 hour hold period, the contents were heated to 60°C. and held for 5 hours, where the level of free isocyanate was measuredto be 11.85%. A premixture of 2480g of Permanol KM10-1733 and 2480g ofNiax PPG 1025 (Union Carbide) were added all at once, and the contentswere heated to 90° C. After 1 hour, 322.42g isodecyl acrylate were addedand the contents were held at 90° C. for an additional 6 hours, when thelevel of free isocyanate was measured to be 0.01%.

Oligomer 2

1627.98 g isophorone diisocyanate, 1439.80 g isodecyl acrylate, 2.00 gphenothiazine, and 4.73 g dibutyltin dilaurate were charged to a 12liter round bottom glass flask fitted wtih a stirrer, dry air sparge,reflux condenser, thermometer, addition funnel, and a heating mantle.477.24 g 2-hydroxyethyl acrylate were added over a period of 90 minuteswith the temperature rising from 28°-34° C. The flask contents wereheated to 40° C., and held for 2 hours, when the level of freeisocyanate was measured to be 12.1%. A premixed solution of 2466.90 gPermanol KM10-1733 and 2467.10 g PolyTHF 1000 (BASF) were added all atonce. 321.50 g isodecyl acrylate were added and the contents were heatedto 90° C. and held for 6 hours, when the level of free isocyanate wasmeasured to be 0%.

Oligomer 3

145.99 g Isophorone diisocyanate, 239.71 g isodecyl acrylate, 0.25 g BHTand 0.52 g dibutyltin dilaurate were charged to a 2 liter round bottomglass flask fitted with a stirrer, thermometer, reflux condenser, dryair sparge, addition funnel, and a heating mantle on a thermostaticallycontrolled automatic jack. 23.16 g 2-hydroxyethyl acrylate were addedover a 90 minute period from the addition funnel with the temperatureremaining constant at 25°-26° C. The contents were heated to 40° C.after the addition, and then held for 2 hours, when the level of freeisocyanate was measured to be 10.9%. 504.91 g Permanol KM10-1733 wereadded all at once, the contents were heated to 80° C., and 49.47 gisodecyl acrylate were added. After sitting at 25° C. for 2.5 days, thelevel of free isocyanate was measured to be 0.04%.

Oligomers 1, 2 and 3 were formulated, cured and evaluated by thepractices utilized in Example 1. The formulations and results of theevaluations are set forth in Table IV below.

                  TABLE IV                                                        ______________________________________                                                    Coating X                                                                             Coating Y Coating Z                                       ______________________________________                                        Oligomer 1              64                                                    Oligomer 2    68                                                              Oligomer 3                        42.68                                       Purified Lucirin TPO                                                                        3         3                                                     Lucirin TPO                       2.98                                        Irganox 1035            0.5       0.5                                         Tinuvin 292   0.5       0.5       0.5                                         A-189*        0.5       0.25      0.25                                        Z-6040**      0.5       0.25                                                  Photomer 4003***        31.5                                                  Aronix M-113                      52.6                                        Tripropyleneglycol                0.5                                         diacrylate                                                                    PEA           2.7                                                             Iraganox 245  0.5                                                             Modulus, MPa  2.3       1.7       1.1                                         Cure Speed, J/cm.sup.2                                                                      0.45      .32       0.37                                        Adhesion, gf dry/wet                                                                        89/39     25/14     62/22                                       ______________________________________                                         *6-mercaptopropyltrimethoxysilane                                             **y-glycidoxypropyltrimethoxysilane                                           ***Same structure as Aronix M113                                         

This invention has been described in terms of specific embodiments setforth in detail, but it should be understood that these are by way ofillustration only and that the invention is not necessarily limitedthereto. Modifications and variations will be apparent from thedisclosure and may be resorted to without departing from the spirit ofthe invention, as those skilled in the art will readily understand.Accordingly, such variations and modifications of the disclosed productsare considered to be within the purview and scope of the invention andthe following claims.

We claim:
 1. A photocurable liquid coating composition adapted toprovide a primary coating for an optical glass fiber comprising: (1)about 30 to about 80 weight percent, based on the total weight of thecoating composition, of an acrylate-terminated polyurethane having anumber average molecular weight of about 2,500 to about 8,000 daltonsand being the reaction product of (i) a prepolymer having a numberaverage molecular weight of about 700 to about 2,000 daltons wherein theprepolymer is selected from the group consisting of polycarbonates andmixtures of polycarbonates and polyethers having an average of at leasttwo groups that are reactive with the isocyanate group, (ii) adiisocyanate and (iii) a hydroxy acrylate; (2) about 20 to about 60weight percent of an acrylate of an unsubstituted of C₇ -C₁₀ alkylsubstituted phenol that is alkoxylated with a C₂ -C₄ alkylene oxide andcontains about 1 to about 5 moles of the oxide per mole of the phenol;and (3) about 5 to about 30 weight percent of at least one alkylacrylatehaving a T_(g) below about -45° C.
 2. The coating composition inaccordance with claim 1 wherein the acrylate of the alkoxylated phenolis alkoxylated with ethylene oxide.
 3. The coating composition inaccordance with claim 1 wherein the acrylate of the alkoxylated phenolcontains about 3.5 to about 4 moles of the oxide per mole of phenol. 4.The coating composition in accordance with claim 3 wherein the acrylateof the alkoxylated phenol is alkoxylated with ethylene oxide.
 5. Thecoating composition in accordance with claim 1 wherein the acrylate ofthe alkoxylated phenol is substituted with a C₈ -C₉ alkyl group.
 6. Thecoating composition in accordance with claim 1 wherein the acrylate ofthe alkoxylated phenol is present in an amount in the range of about 20to about 35 weight percent and the acrylated polyurethane is present inan amount in the range of about 30 to about 60 weight percent.
 7. Thecoating composition in accordance with claim 1 wherein the prepolymer is(a) a polycarbonate diol produced from an alkylene diol having about 2to about 12 carbon atoms or (b) a polycarbonate copolymer of apolyalkylene oxide and the alkylene diol.
 8. The coating composition inaccordance with claim 1 wherein the prepolymer is (a) a polycarbonatediol produced from an alkylene diol having about 4 to about 8 carbonatoms or (b) a polycarbonate copolymer of a polyalkylene oxide and thealkylene diol.
 9. The coating composition in accordance with claim 1wherein the prepolymer has a number average molecular weight of about800 to about 2,000 daltons.
 10. The coating composition in accordancewith claim 1 wherein the polyurethane has a number average molecularweight of about 3,000 to about 7,000 daltons.
 11. The coatingcomposition in accordance with claim 1 further including about 1 toabout 15 weight percent of a monethylenically unsaturated materialhaving a T_(g) greater than about 40° C. and a strong capacity forhydrogen bonding.
 12. The coating composition in accordance with claim11 wherein the monoethylenically unsaturated material is an N-vinylmonomer.
 13. The coating composition in accordance with claim 1 furtherincluding about 2 to about 4 weight percent of a monoethylenicallyunsaturated material having a T_(g) greater than about 40° C. and astrong capacity for hydrogen bonding.
 14. The coating composition inaccordance with claim 1 wherein the prepolymer has an average of atleast about two groups that are reactive with the isocyanate group andthe mole ratio of prepolymer:diisocyanate: hydroxy acrylate utilized toproduce the acrylated polyurethane is in a range of about 1:2:2,respectively, to about 5:6:2, respectively.
 15. A photocurable liquidcoating composition adapted to provide a primary coating for an opticalglass fiber comprising: (1) about 30 to about 60 weight percent, basedon the total weight of the coating composition, of anacrylate-terminated polyurethane having a number average molecularweight of about 2,500 to about 8,000 daltons and being the reactionproduct of (i) a prepolymer having a number average molecular weight ofabout 700 to about 2,000 daltons, the prepolymer being (a) apolycarbonate diol produced from an alkylene diol having about 2 toabout 12 carbon atoms or (b) a polycarbonate copolymer of an alkyleneoxide and the alkylene oxide diol, (ii) a diisocyanate and (iii) ahydroxy acrylate; (2) about 20 to about 60 weight percent of an acrylateof an unsubstituted or C₈ -C₉ alkyl substituted phenol that isalkoxylated with a C₂ -C₄ alkylene oxide and contains about 1 to about10 moles of the oxide per mole of the phenol; and (3) about 5 to about30 weight percent of at least one alkylacrylate having a T_(g) belowabout -45° C.
 16. The coating composition in accordance with claim 15wherein the alkylene diol of (i) has about 4 to about 8 carbon atoms.17. The coating composition in accordance with claim 15 wherein theacrylate of the alkoxylated phenol is alkoxylated with ethylene oxide.18. The coating composition in accordance with claim 15 wherein theacrylate of the alkoxylated phenol contains about 3.5 to about 4 molesof the oxide per mole of phenol.
 19. The coating composition inaccordance with claim 15 wherein the acrylate of the alkoxylated phenolis alkoxylated with ethylene oxide.
 20. The coating composition inaccordance with claim 15 wherein the acrylate of the alkoxylated phenolis present in an amount in the range of about 10 to about 35 weightpercent.
 21. The coating composition in accordance with claim 15 furtherincluding about 1 to about 15 weight percent of a monoethylenicallyunsaturated material having a T_(g) greater than about 40° C. and astrong capacity for hydrogen bonding.
 22. The coating composition inaccordance with claim 15 wherein the mole ratio of polycarbonatediol:diisocyanate: hydroxy acrylate utilized to produce the polyurethaneis in a range of about 1:2:2, respectively, to about 5:6:2,respectively.